Camshaft adjusters are used in internal combustion engines for varying the control times of the combustion chamber valves, in order to variably shape the phase relation between a crankshaft and a camshaft in a defined range of angles between a maximum advanced position and a maximum retarded position. Adapting the control times to the current load and rotational speed reduces the consumption and the emissions. For this purpose, camshaft adjusters are integrated into a drive train by which torque is transmitted from the crankshaft to the camshaft. This drive train can be constructed, for example, as a belt drive, chain drive, or gearwheel drive.
In a hydraulic camshaft adjuster, the driven element and the drive element form one or more pairs of pressure chambers that act in opposite directions and can be pressurized with hydraulic medium. The drive element and the driven element are arranged coaxial to each other. By filling and emptying individual pressure chambers, a relative movement is generated between the drive element and the driven element. A spring causes rotation between the drive element and the driven element forces the drive element in a preferred direction relative to the driven element. This preferred direction can be in the same direction as or opposite the direction of rotation.
One structural type of hydraulic camshaft adjuster is the vane cell adjuster. The vane cell adjuster has a stator, a rotor, and a drive wheel with external teeth. The rotor is constructed as the driven element and usually can be locked in rotation with the camshaft. The drive element includes the stator and the drive wheel. The stator and the drive wheel are locked in rotation with each other or are alternatively constructed as one part with each other. The rotor is arranged coaxial to the stator and within the stator. The rotor and the stator form, with their vanes extending in the radial direction, oil chambers that act in opposite directions and can be pressurized by oil pressure and allow a relative rotation between the stator and the rotor. The vanes are formed either integrally with the rotor or the stator or arranged as “inserted vanes” in grooves of the rotor or the stator provided for this purpose. The vane cell adjusters further have various sealing covers. The stator and the sealing cover are secured with each other by means of several screw connections.
Another structural type of hydraulic camshaft adjuster is the axial piston adjuster. Here, a displacement element is shifted in the axial direction via oil pressure, wherein this element generates a relative rotation between a drive element and a driven element through the use of helical teeth.
From WO 2011 138 136 A1 it is known to arrange a volume accumulator in a camshaft adjuster, wherein, in the case of an under-pressure in the pressure chambers, hydraulic fluid can be drawn from the volume accumulator into the pressure chambers. For realizing this function, the camshaft adjuster has several non-return valves that have a U-shaped construction and allow a flow of hydraulic medium from the volume accumulator inside the camshaft adjuster to the pressure chambers.